The present invention generally relates to an internal combustion engine with single overhead camshaft and, more particularly, to the internal combustion engine of a type wherein intake and exhaust valves are driven by a single overhead camshaft generally in opposite sense with respect to each other through rocker arms.
The single overhead camshaft engine, or SOHC engine for short, is not a recent development and has long been well known in the art, generally in the following two models:
As exemplified by the engine disclosed in, for example, the Japanese Laid-open Patent Publication No. 55-151104, published Nov. 25, 1980, the first model makes use of paired intake valves and paired exhaust valves both supported in the cylinder head for movement in a direction generally parallel to the longitudinal axis of the engine cylinder, and also of a single rocker arm support shaft supported by the cylinder head so as to extend between the paired intake valves and the paired exhaust valves in a direction perpendicular to the longitudinal axis of the engine cylinder. The rocker arm support shaft carries first paired rocker arms for driving the respective intake valves and second paired rocker arms for driving the respective exhaust valves, said first and second paired rocker arms extending laterally outwardly from the rocker arm support shaft in opposite directions away from each other. The single overhead camshaft, having cams for driving the intake and exhaust valves through the associated rocker arms, extends immediately above the rocker arm support shaft parallel thereto.
The paired intake ports and the paired exhaust ports, which are selectively opened and closed by the paired intake valves and the paired exhaust valves, are defined in a bottom wall of the cylinder head so as to confront the cylinder bore, defined in the cylinder block and accommodating the reciprocateable piston. The area of the cylinder head bottom wall, where all the intake and exhaust ports are opened and which confronts the cylinder bore, is inwardly recessed or concaved a slight distance, for example, 3 to 4 mm at maximum, so as to define the top of the combustion chambers, and, on the other hand, the piston has its top end face axially inwardly concaved.
The engine disclosed in Publication No. 55-151104 is described as employed in the form of either a gasoline powered engine or a diesel engine and, for this purpose, the use is disclosed of either the ignition plug or the fuel injector nozzle. Regardless of the type of fuel used, a socket for the support of either the ignition plug or the fuel injector nozzle is defined in the cylinder head bottom wall so as to extend at an angle relative to the longitudinal axis of the engine cylinder and has one of its opposite ends opening into the combustion chamber at a location lying on the longitudinal axis of the engine cylinder, a substantially intermediate portion of said socket extending diagonally upwardly between the intake valves.
The other model is exemplified by the engine disclosed in, for example, the Japanese Laid-open Patent Publication No. 57-102506, published June 25, 1982. Except that that area of the cylinder head bottom wall which confronts the cylinder bore is inwardly concaved in a depth greater than that disclosed in the first mentioned publication, and that the paired intake valves and the paired exhaust valves used in the last mentioned publication are inclined so as to move in respective directions diverging away from each other in a direction upwardly of the cylinder head, the engine disclosed in the last mentioned publication is similar to that disclosed in the first mentioned publication. The camshaft is, however, positioned between the paired intake valves and the paired exhaust valves and closer to the cylinder head bottom wall, while the paired rocker arms for the paired intake valves and those for the exhaust valves are positioned above the camshaft.
It has been found, however, that both models have their own problems. More specifically, in the case of the first mentioned model, since that surface area of the cylinder head bottom wall, which confronts the cylinder bore and constitutes a top wall for the combustion chamber, is inwardly concaved or recessed in such a manner that the distance as measured between the plane of a surface of the cylinder block, at which the cylinder bore is opened, and the top wall of the combustion chamber in a direction parallel to the longitudinal axis of the cylinder bore, increases progressibely from the perimeter of the cylinder bore towards the longitudinal axis of the cylinder bore, a squash area, that is, an area of the combustion chamber which is delimited between the top end face of the piston and the top wall of the combustion chamber when the piston has been moved to a top dead center position, is so small that the combustible air-fuel mixture within the combustion chamber can hardly be vigorously squashed by the piston arriving at the top dead center position.
Moreover, since the socket for the support of either the ignition plug or the fuel injector nozzle extends diagonally downwards between the intake ports, the space available for the formation of the intake ports in the cylinder head bottom wall is correspondingly limited, with no freedom of design of the increased intake ports consequently available.
In the case of the last mentioned model, in addition to the above discussed problem attributable to the inwardly concaved surface area defining the top wall of the combustion chamber, there is another problem in that for each of the rocker arms for the exhaust valves, a stud shaft is employed for supporting the respective rocker arm. The use of the separate stud shafts for supporting the rocker arms for the exhaust valves is necessitated to provide the space between the stud shafts, through which the ignition plug can be inserted into the plug support socket. This means that, when the engine has a plurality of engine cylinders, the stud shafts, for the support of the respective rocker arms for the paired exhaust ports, are necessitated in a number double the number of the engine cylinders.